Yeah, this is what Jim McCarthy calls Beware of a guy in a room (point 6). Curiously, it's usually the most brilliant developer who goes dark. Years ago, the top programmer of a company we were dealing with got away with saying "it will be ready next month" for 18 months without ever allowing anyone to see his code until it was finished! All developers, no matter how brilliant, must make their code available for public review in modest (fortnightly, say) increments.

Update: see also: Beware of a guy in a room (youtube)